Apparatus for spraying liquids, and disposable containers and liners suitable for use therewith

ABSTRACT

A spray gun ( 1 ) has a fluid reservoir ( 11 ) which contains a removable liner ( 13 ). The liner ( 13 ), which may be thermo/vacuum-formed from a plastic material, is a close fit within the interior of the reservoir and collapses as fluid is withdrawn from within the liner during operation of the gun. Preferably, the liner has a comparatively-rigid base and is capable of standing, unsupported, outside the reservoir. The side walls of the liner are preferably thin in comparison to the base and can be collapsed for disposal of the liner. The reservoir ( 11 ) has a removable lid ( 15 ) and is capable of standing, inverted, on its own so that it can be filled with fluid. The lid ( 15 ) also functions to secure the liner ( 13 ) in the reservoir and, at the end of a spraying operation, the lid ( 15 ) and the liner ( 13 ) are removed together from the reservoir ( 11 ) and discarded, thereby simplifying the cleaning of the spray gun.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. Ser. No. 09/508883,filed Jul. 23, 1999, now allowed; which was a national stage filingunder 35 U.S.C. 371 of PCT/US98/00796, filed Jan. 14, 1998, whichInternational Application was published by the International Bureau inEnglish on Jul. 30, 1998; which claims priority to GB 9701447.6, filedJan. 24, 1997, and GB 9712784.9, filed Jun. 18, 1997; the disclosure ofwhich is herein incorporated by reference.

[0002] The present invention relates to containers, more especially,disposable containers and to containers which can function as liners.The invention also relates to apparatus for spraying liquids (forexample, spray guns) and, more especially, to the liquid containers orreservoirs of such apparatus.

[0003] There are many uses, in many different fields, for disposablecontainers. For example, many goods are packaged in disposablecontainers (e.g. bags) either before or after purchase. When thedisposable container is a plastic bag, it will often be re-used by thepurchaser as a disposable liner for another receptacle, for example arefuse bin. In some cases, disposable liners are produced specificallyfor use in other, re-usable, receptacles: in those cases, the liner maybe intended to aid disposal of the contents of the receptacle (as in thecase of a liner in a refuse bin); to protect the receptacle or itscontents; or to facilitate, or even eliminate, the cleaning of thereceptacle.

[0004] The use of a liner in a receptacle in which a substance likeglue, paint or plaster is mixed or contained for use can be particularlyadvantageous, in terms of facilitating the cleaning of the receptacleafter use and of preventing substances in the receptacle from beingcontaminated by the remains of other substances. Receptacles in whichpaints are mixed or contained for use, for example, must be clean toensure that the colour or quality of the paint is not altered by tracesof other substances: that is particularly important, as explained above,when a vehicle is being re-painted and the paint is required to match anexisting one. To avoid contamination problems when mixing paints, it isoften the practice in vehicle body shops to use disposable waxed papercups as mixing containers, particularly when only a small amount ofpaint is required. An alternative approach, proposed in U.S. Pat. No.4,383,635, involves the provision of a disposable container which, foruse, is located in a re-usable frame-like receptacle.

[0005] In the field of spray guns, it has been proposed for variousreasons that a disposable liner should be used in the reservoir of thegun (see U.S. Pat. Nos. 3,211,324, 3,255,972, 4,151,929, 4,951,875 and5,143,294, and EP-A-0 678 334). Guns for spraying liquids (e.g. paints,garden chemicals etc.) are generally well known and typically comprise areservoir in which a liquid to be dispensed is contained, and a spraynozzle through which the liquid is dispensed, under pressure, under thecontrol of a trigger mechanism. The liquid may be fed from the reservoirunder gravity and/or it may be entrained in a stream of pressurizedfluid, for example air or water, which is supplied to the gun from anexternal source.

[0006] When a user wishes to change the liquid in the reservoir of aspray gun, it is usually necessary to clean the gun very thoroughly toensure that no traces of the old liquid remain in the gun to contaminatethe new liquid. That applies particularly to paint spray guns becauseany traces of an old batch of paint remaining in a gun may affect thecolour of a new batch of paint to the extent that the new batch of paintbecomes useless. This can cause problems especially in vehicle bodyshops where the paint applied to a vehicle is often required to matchexisting paint work exactly. Alternatively, if paint residues have beenallowed to dry within the gun, they may flake and contaminate the newbatch of paint. The cleaning of spray guns is, however, a comparativelycomplex and time consuming operation. Moreover, in the case of paintspray guns, the cleaning operation involves the use of comparativelylarge amounts of solvents which, for environmental reasons, should behandled and disposed of with care. That, in turn, can add substantiallyto the cost of a painting operation. It has already been suggested (see,for example, EP-A-0 678 334 mentioned above) that the use of adisposable liner in the paint reservoir (i.e. the paint pot) of a spraygun can simplify the cleaning of the gun and reduce the amount ofsolvent required.

[0007] The present invention is concerned with the provision of acontainer which is sufficiently inexpensive to be disposable and whichcan preferably be collapsed when it is to be disposed of but which,nevertheless, is comparatively easy to handle and to fill when in use.The invention is concerned, more especially, with the provision of sucha container which is suitable for use as a liner in another receptacle.The present invention is also concerned with enabling the cleaning ofspray guns and like apparatus to be simplified, and with therebyenabling the time and expense associated with that operation to bereduced.

[0008] The present invention provides a container comprising side wallsand a comparatively-rigid base thermo/vacuum-formed from a plasticsmaterial; wherein the side walls are thin in comparison to the base andare collapsible, but the container is capable of standing, unsupported,on the base with the side walls extended and upright.

[0009] More especially, the present invention provides a containercomprising a base, and side walls extending from the base; wherein thebase and side walls are thermo/vacuum formed together from a plasticsmaterial in such a manner that the base is comparatively rigid and theside walls are thin in comparison to the base and are collapsible butthe container is capable of standing unsupported, on the base with theside walls extended and upright.

[0010] A container in accordance with the invention may be used as aliner for a receptacle, the liner having a shape which corresponds tothe interior of the receptacle. As a modification, the invention alsoprovides, in combination with a receptacle, a disposable liner whichfits within and has a shape corresponding to the interior of thereceptacle wherein the liner is thermo/vacuum formed from a plasticsmaterial. The liner is preferably, but not necessarily, collapsible.

[0011] The present invention also provides a spray gun comprising afluid reservoir; a removable, collapsible, liner which has a shapecorresponding to, and is a close fit within, the interior of thereservoir; and a spray nozzle for dispensing fluid from within theliner; wherein the liner collapses when fluid is withdrawn from withinthe liner during operation of the gun.

[0012] Also in accordance with the invention, there is provided a spraygun comprising a fluid reservoir having a removable lid located in anopening in the reservoir; a removable liner located within the reservoirand secured to the reservoir, by the lid, at the periphery of theopening; and a spray nozzle for dispensing fluid from within the liner;wherein the liner is removable from the reservoir together with the lid.

[0013] The present invention also provides a gravity-fed spray guncomprising a fluid reservoir having a removable lid located in anopening in the reservoir; and a spray nozzle for dispensing fluid drawnfrom within the reservoir through an outlet in the lid; wherein thereservoir is removable from the gun and is capable of standing on itsown to enable fluid to be loaded into the reservoir through the opening.

[0014] The invention further provides a spray gun comprising a fluidreservoir; and a spray nozzle for dispensing fluid from within thereservoir; the reservoir comprising a self-supporting container which isremovable from the gun and is collapsible for disposal.

[0015] In accordance with another aspect of the invention, there isprovided a fluid reservoir for attachment to a spray gun, the reservoirhaving a removable lid which is located in an opening in the reservoirand in which is formed a fluid outlet for the reservoir; the reservoirincluding a removable, collapsible, liner which has a shapecorresponding to, and is a close fit within, the reservoir; wherein theliner is secured to the reservoir by the lid at the periphery of theopening and is removable from the reservoir together with the lid. Theinvention also provides a fluid reservoir for attachment to a spray gun,the reservoir having a removable lid which is located in an opening inthe reservoir and in which is formed a fluid outlet for the reservoir,the fluid outlet being shaped for attachment to the spray gun; and aclosable air vent in the end of the reservoir remote from the lid.

[0016] In accordance with yet another aspect of the invention, there isprovided a liner for use in the reservoir of a spray gun, the linerbeing formed from a plastic material and being a close fit within thereservoir; the liner having a comparatively rigid base, and side wallswhich are thin in comparison to the base and are collapsible.

[0017] The present invention also provides a spray gun comprising afluid reservoir, and a spray nozzle for dispensing fluid from within thereservoir, the reservoir having a removable lid and including aremovable, generally conical, mesh filter secured in the reservoir bythe lid.

[0018] The present invention also provides a gravity-feed spray guncomprising a fluid reservoir, and a spray nozzle for dispersing fluidfrom within the reservoir, the reservoir having a removable lid and aremovable liner secured in the reservoir by the lid.

[0019] The term “thermo/vacuum-forming” as used herein means a processby which a sheet of material is heated to a softened condition andformed into a required shape, defined by a mould, while in that softenedcondition. It includes the case in which the application of adifferential air pressure is used to assist in forming the material intothe required shape and, in particular, includes the case in which avacuum is produced on one side of the material to assist in forming itinto the required shape (also known simply as “vacuum-forming”).

[0020] The term “collapsible” as used herein with reference to the sidewalls of a container/liner in accordance with the invention indicatesthat the side walls can be distorted so that, by the application ofmoderate pressure (e.g. hand pressure), the rim of the container can bepushed towards the base of the container, without the side walls beingruptured.

[0021] The term “paint” is used herein to include all forms ofpaint-like coating materials that can be applied to a surface using aspray gun, whether or not they are intended to colour the surface. Theterm includes, for example, primers, base coats, lacquers and similarmaterials.

[0022] By way of example only, embodiments of the invention will bedescribed with reference to the accompanying drawings, in which:

[0023]FIG. 1 is a perspective view of a prior art spray gun, shownpartly-disassembled so that it can be filled with paint;

[0024]FIG. 2 shows the components of an alternative form of paintreservoir for the gun of FIG. 1, in an exploded condition;

[0025]FIG. 3 shows the paint reservoir of FIG. 2 in an assembledcondition, with an adapter for connecting the reservoir to a spray gun;

[0026]FIG. 4 shows a longitudinal cross-section through the paintreservoir and the adapter of FIG. 3;

[0027]FIG. 5 shows the paint reservoir of FIG. 4 being attached to aspray gun;

[0028]FIG. 6 shows the paint reservoir of FIG. 4 in use on a spray gun;

[0029]FIG. 7 shows components of the paint reservoir of FIG. 4 beingremoved after use;

[0030]FIG. 8 is similar to FIG. 2 but shows a modified form of paintreservoir;

[0031]FIG. 9 shows a longitudinal cross-section through an alternativeform of lid for the paint reservoirs of FIGS. 2 to 4 and 8;

[0032]FIG. 10 is similar to FIG. 2 but shows another modified form ofpaint reservoir;

[0033]FIG. 11 shows part of a longitudinal cross-section through thepaint reservoir of FIG. 10;

[0034]FIG. 12 shows a spray gun similar to that of FIG. 1 but with analternative form of paint reservoir;

[0035]FIG. 13 shows the gun of FIG. 12 with a modified form of paintreservoir;

[0036]FIG. 14 illustrates a modification to the reservoir of the gun ofFIG. 13.

[0037]FIG. 15 is a view, similar to FIG. 3, of an alternative form ofpaint reservoir;

[0038]FIGS. 16 and 17 show modified forms of a component of FIG. 15;

[0039]FIG. 18 illustrates the use of a holder for the paint reservoir ofFIG. 15;

[0040]FIG. 19 is a perspective view of a liner/container in accordancewith the invention;

[0041]FIG. 20 is a similar view but showing the liner/container in theprocess of being collapsed for disposal;

[0042]FIG. 21 (a) to (c) is a diagrammatic illustration of a method forproducing a liner for the paint reservoirs of FIGS. 2 to 4, and 10;

[0043]FIG. 22 illustrates a modification of the method of FIG. 21;

[0044]FIG. 23 shows a paint-mixing pitcher; and

[0045]FIG. 24 shows a liner in accordance with the invention, for usewith the pitcher of FIG. 23.

[0046]FIG. 1 of the drawings illustrates a typical prior art paint spraygun 1 of the gravity-feed type. The gun 1 comprises a body 2, a handle 3which extends downwards from the rear end of the body, and a spraynozzle 4 at the front end of the body. The gun is manually-operated by atrigger 5 which is pivotally-mounted on the sides of the gun. The paintreservoir, or paint pot, 6 which contains paint (or similar material) tobe discharged by the gun, is located on the top of the body 2 andcommunicates with an internal passageway (not visible) for compressedair, which extends through the gun from a connector 7 at the lower endof the handle 3 to the nozzle 4. In use, the connector 7 is connected toa source of compressed air (not shown) so that, when the user pulls onthe trigger 5, compressed air is delivered through the gun to the nozzle4 and entrains and atomizes paint which is being delivered under gravityfrom the pot 6. The paint is then discharged through the nozzle 4 withthe compressed air, as a spray.

[0047] The paint which is contained in the pot 6 is often mixed by hand(for which a separate receptacle, for example a jug, is required), andpoured into the pot. To ensure that there are no unwanted particles inthe paint, which would spoil the finish of the painted surface, thepaint is usually poured into the pot 6 through a filter. FIG. 1 showsthe cap 8 of the pot 6 removed for this purpose, and a conical filter 9about to be positioned on the open end of the pot. The filter 9 is shownas being a known type of disposable conical filter, having solid sidesand a filter mesh portion 10 at the pointed end of the cone. When thepot 6 has been filled with paint, the filter 9 is removed and discarded,and the cap 8 of the pot is replaced. If the filter 9 is a reusablefilter then, like the gun, it should be cleaned thoroughly before it isused with a different liquid (e.g. a paint of a different colour or aliquid having a different chemical composition).

[0048]FIG. 2 illustrates the components of an alternative form of paintpot 11 which can be used on the gun 1 of FIG. 1 (or any similar gun)instead of the pot 6. The alternative form of paint pot 11 is shownassembled in FIG. 3 and (in cross-section) in FIG. 4.

[0049] The paint pot 11 comprises an open container 12, comparable insize to a conventional paint pot of a hand-held spray gun, having an airhole 12A in its base and provided with a disposable liner 13. The liner13 corresponds in shape to (and is a close fit in) the interior of thecontainer 12 and has a narrow rim 14 at the open end which sits on thetop edge of the container. The container 12 also has a disposable lid 15which is a push-fit in the open end of the liner 13. The lid 15 has acentral aperture 16 (FIG. 4) from which extends a connector tube 17provided, at its end, with outward extensions 18 forming one part of abayonet connection. The aperture 16 is covered by a filter mesh 19 whichmay be a push fit into the aperture or may be an integral part of thelid 15. The lid 15 is held firmly in place on the container 12 by anannular collar 20 which screws onto the container, on top of the lid.

[0050] The paint pot 11 is attached to the spray gun 1 through the useof an adapter 21 shown, separated from the paint pot, in FIG. 3 and (incross-section) in FIG. 4. The adapter 21 is a tubular component which,at one end 22, is formed internally with the other part of the bayonetconnection for attachment to the connector tube 17 of the paint pot 11.At the other end 23, the adapter is shaped to match the standardattachment of the spray gun paint pot (typically a screw thread).

[0051] The liner 13 of the paint pot 11, as already mentioned,corresponds in shape to the interior of the container 12 and has anarrow rim 14 at the open end which sits on the top edge of thecontainer. As described below, the liner is self-supporting but is alsocollapsible and, preferably, has a comparatively rigid base 13A andcomparatively thin side walls 13B so that, when it collapses, it is inthe longitudinal direction by virtue of the side walls collapsing ratherthan the base. In addition, the liner 13 has no pleats, corrugations,seams, joints or gussets, and also no groove at the internal junction ofthe side walls 13B with the base 13A. A liner of that type will bedescribed in greater detail later with reference to FIGS. 19 and 20.Also described below is a thermo-forming process by which such a linercan be produced.

[0052] The container 12 of the paint pot 11 is formed from a plasticmaterial, for example polyethylene or polypropylene, and may betranslucent (as shown in FIG. 2) or opaque, and of any suitable size.For use with a paint spray gun, containers having a capacity of 250, 500or 800 ml could typically be used, although other sizes could be used ifrequired. The lid 15 is also formed from a plastic material, forexample, polyethylene or polypropylene, and may be formed by aninjection moulding process. The lid may be translucent or opaque and maybe coloured. The collar 20 may be a moulded plastic component, or it maybe a machined metal (for example, aluminium) component. The adapter 21may be a machined metal component and may, for example, be formed fromaluminium and anodised.

[0053] To use the paint pot 11, the adapter 21 is attached (at the end23) to the spray gun and is left in position. Then, with the paint pot11 disassembled as shown in FIG. 2, the liner 13 is pushed inside thecontainer 12. Paint is then put into the container, the lid 15 is pushedinto place and the collar 20 is screwed down tightly to hold the lid inposition. The top portion of the liner 13 is then trapped between thelid 15 and the container 12, and the liner rim 14 is trapped between thetop edge of the container and the collar 20, as shown in FIG. 4.Advantageously, the lid 15 is formed with barbs (not visible) on itssurface to engage and hold the top of the liner. The spray gun 1 is theninverted from its normal operating position so that the end of theconnector tube 17 can be attached to the adapter 21 as illustrated inFIG. 5, after which the gun can be returned to its normal position(illustrated in FIG. 6) and is ready for use in the usual way. As paintis removed from within the liner 13, the sides of the liner collapse asa result of the decreased pressure within the liner. The base of theliner, being more rigid, retains its shape so that the liner tends tocollapse in the longitudinal rather than the transverse directionthereby reducing the possibility of pockets of paint being trapped inthe liner.

[0054] The user can choose to evacuate the air from within the liner 13before operating the spray gun 1 although that is not essential. Itdoes, however, increase the range of angles at which the gun willfunction satisfactorily since there is no risk of air entering the gunfrom the paint pot 11. To evacuate the air from within the liner 13, thetrigger 5 of the gun should be actuated while the gun is still in theposition shown in FIG. 5.

[0055] After use, when the gun is to be cleaned, the gun can bere-inverted and the trigger 5 can be actuated briefly to allow paintwithin the gun to drain back into the liner in the pot 11. The pot 11 isthen removed from the gun by detaching the connector tube 17 from theadapter 21 (which remains on the gun). The collar 20 is removed from thecontainer 12, and the lid 15 is then pulled out, bringing with it thecollapsed liner 13, as shown in FIG. 7. The lid (including the filter19) and liner are discarded, leaving the container 12 and collar 20clean and ready for re-use with a fresh liner and lid. Only the gunitself needs to be cleaned, resulting in a substantial reduction in theamount of solvent used. The risk of unused paint spilling from the pot11 is also substantially reduced because the liner 13 is removed anddiscarded with the lid 15 in place. Moreover, because the liner isdiscarded in a collapsed condition, the amount of space required forcollection of used liners is minimized.

[0056] Because the liner 13, as described above, is an accurate fitinside the container 12 and has a smooth internal surface, it ispossible to mix paint in the container 12 itself rather than in aseparate receptacle. In that way, cleaning of a separate mixingreceptacle can be eliminated to achieve a further reduction in theamount of solvent used. That possibility does not exist when using agravity-feed gun with a conventional paint pot, as shown at 6 in FIG. 1,because the latter is open at both ends. The possibility of the liner 13being punctured or damaged by the mixing implement is minimized, firstbecause the liner fits inside the container 12 exactly and, second,because the self-supporting nature of the liner (described below) meansthat it is less likely to be dragged around inside the container duringthe mixing process. To facilitate the use of the container 12 as amixing receptacle, the side walls of the container may be provided withmarkings 25 (FIGS. 2 and 3) enabling the volume of the contents of thecontainer to be determined. The general shape of the container 12 and,in particular, the fact that it is flat-bottomed and stable when in theorientation shown in FIG. 2 makes it particularly suitable for use as amixing receptacle, as does the fact that it is translucent as alreadydescribed. If, however, the container 12 is opaque, it could be formedwith slots in the side walls, through which the liner 13 could be viewedto enable the user of the spray gun to assess the amount of paint in thepot 11 at any time.

[0057] When paint is mixed in the container 12, the inclusion of thefilter mesh 19 in the container lid 15 prevents unwanted particles inthe paint from entering the spray gun. The mesh 19 can be omitted,however, if the paint is textured, or if it is mixed in a separatereceptacle and strained when it is transferred to the lined container 12or if the presence of contaminants in the paint is unimportant.

[0058] Although the collar 20 of the paint pot 11 is described above asbeing a separate item, it could be combined with the lid 15, in whichcase it would also be disposable. As a further alternative, the lid 15(with the connector tube 17 and the mesh 19) could be formed as anintegral part of the liner 13, to which it could be connected by a hingejoint 26 as illustrated in FIG. 8. In that case, there is no need forthe lid to fit inside the mouth of the liner to ensure that the lid andliner will be removed together from the container after use: however,that would still be necessary if the lid were required to remain inplace in the liner after use. As yet another alternative, the collar 20could be replaced by a band secured around the top of the pot 11 to holdthe lid 15 and liner 13 in place. The band could be secured to the pot11 and could, for example, be formed from rubber or be part of a metalclip arrangement of the type used to secure the tops of jars andbottles.

[0059] If a more positive engagement is required between the lid 15 ofFIGS. 2 to 4 and the liner 13, the lid could be a snap fit with theliner instead of a push-fit as shown. The liner could, for example, beformed with an internal circumferential rib positioned to engage in acorresponding groove on the adjacent surface of the lid.

[0060] As yet a further alternative, the push-in lid 15 could bereplaced by a lid 27 having the form shown in FIG. 9. The lid 27 is alsoa push-fit inside the liner but is generally conical in shape and at itsupper end 28, corresponds in shape to the end of the connector tube 17of FIGS. 2 to 4 so that it will engage in the same adapter 21. The lid27 has an outwardly-extending rim 29 which will sit on top of the linerrim 14, and a shaped portion 29A which will engage the internal surfaceof the liner. The form of the shaped portion 29A allows the lid 27 to bepushed into the mouth of the liner and also provides a recess 29B intowhich the edge of the liner can contract so that the lid is securelylocated. The form of the shaped portion illustrated in FIG. 9 is notessential, however, and alternatives could be used including, forexample, barbs as described above with reference to the lid 15 of FIG.4. The lid 27 is held in place on the container by a screw-on collar,similar to the collar 20, which will sit on top of the rim 29 of thelid. The lid 27 may incorporate a filter similar to the filter 19 ofFIGS. 2 to 5. Alternatively, in each case, the filter may be generallycylindrical in shape so that it can be inserted into the tubular part ofthe lid from the end adjacent the bayonet connection. In that case, theinternal shaping of the tubular part of the lid should ensure that thefilter remains in position when the spray gun is in use.

[0061] The components of an alternative form of paint pot 30 areillustrated in FIG. 10. The pot 30, like the pot 11 of FIG. 2, comprisesa container 12 and a liner 13. In this case, however, the filter 19 ofthe pot 11 is formed as a separate item 31 having a diametercorresponding to that of the container 12 and including acircumferential sealing gasket 32. In addition, the lid 15 and collar 20of the pot of FIG. 2 are replaced by a generally-conical lid 33 which isa screw-fit onto the container and which, at its upper end has a tubularextension 34 of similar shape to the connector tube 17 of FIG. 3 so thatit will engage in the same adapter 21. The pot 30 is assembled bypushing the liner 13 inside the container 12 and then, after paint hasbeen put into the container, placing the filter 31 on top of thecontainer and securing it in position by screwing down the lid 33. Therim 14 of the liner 13 and the sealing gasket 32 of the filter 31 arethen both trapped between the lid 33 and the container 12, asillustrated in FIG. 11, thereby preventing the leakage of paint from thepot 30 at this location when the pot has been secured to a spray gun andis inverted for use.

[0062] The adapter 21 could be dispensed with by forming the ends of thetubular parts 17, 34 of lids of the containers 11, 30 with screw threadsso that they can engage directly in the standard paint pot attachment onthe spray gun 1.

[0063]FIG. 12 illustrates an alternative spray gun in which the standardpaint pot 6 of the spray gun 1 (see FIG. 1) is retained and is providedwith a liner 35 which fits inside the pot and, preferably, extends intothe connection with the body 2 of the gun to form a liquid-tight sealwith the latter, for example through the use of a flexible O-ring (notvisible) between the gun and the liner. In this case, the liner 35 doesnot collapse when paint is removed from within the pot and may be formedfrom a more rigid material to assist in positioning it within the pot 6.Once in position, the liner 35 is held in place by the cap 8 which isscrewed down onto an outwardly-extending rim 36 at the open end of theliner. The pot 6 of FIG. 12 is additionally provided with a filter 37which is of generally conical shape and formed entirely of mesh materialand which, in use, is positioned inside the liner 35. The filter 37,like the liner 35, has an outwardly-extending rim 38 which lies on topof the liner rim 36 and is likewise held in place by the cap 8 of thepot 6.

[0064] The pot 6 of FIG. 12, unlike the pot 11 of FIG. 3 is intended tobe filled with paint while attached to the spray gun 1. The liner 35 andfilter 37 are placed in position, paint is poured into the pot, and thecap is fitted. During this operation, there is no risk of the filterbeing dislodged and, because the filter is formed entirely of meshmaterial, the user is always able to see the paint level while the paintis being poured into the pot. The gun 1 is then ready for use. All ofthe paint dispensed by the gun passes through the filter 37 and thereis, accordingly, no need for the paint to be filtered when it is beingpoured into the pot 6. After use, the cap 8 unscrewed is to allow thefilter 37 and liner 35 to be removed. The liner 35 is discarded and thefilter 37 is either also discarded or is cleaned, depending on whetheror not it is disposable. The use of the liner 35 again reduces theamount of solvent required to clean the gun 1, with a further reductionbeing possible through the use of a disposable filter 37.

[0065] The filter 37 can have any suitable shape and may, for example,have fluted sides to increase the effective surface area of the filter.

[0066] In a modified arrangement, illustrated in FIG. 13, the liner 35and the filter 37 are combined to form a single unit 39. In this case,the filter is discarded with the liner.

[0067] In each of the arrangements shown in FIGS. 12 and 13, the liner35 and filter 37 can be removed from the pot 6 with the lid 8. In thatcase, it is possible to replace the conventional lid 8 of the pot 6 by adisposable lid so that the lid 8, liner 35 and filter 37 can bediscarded together.

[0068] The disposable unit 39 of FIG. 13 could be modified so that itwould replace the paint pot 6 of the spray gun 1 instead of being fittedinside the paint pot. In that case, the unit 39 could be supplied as asealed cartridge 50 already filled with paint as illustrated in FIG. 14.Externally, the cartridge 50 is similar to the paint pot 6 and can beconnected to the gun 1 in the same way. Because it is sealed, however,the outlet end 51 of the cartridge must be pierced and an air ventprovided, for example at the other end 52 of the cartridge, to allowpaint to flow into the gun. The outlet end 51 of the cartridge 50 could,for example, be pierced by the user before the cartridge (with theoutlet end uppermost) is attached to the (inverted) gun. Alternatively,the gun 1 could be modified so that the outlet end 51 is piercedautomatically when the cartridge 50 is attached to the gun. An air ventat the other end 52 of the cartridge 50 could then be formed after thecartridge has been attached to the gun by piercing that end of thecartridge either manually or, for example, by attaching a separate cap53 which is designed to pierce the cartridge when it is placed inposition. Alternatively, an air vent, which simply needs to be openedwhen the gun is ready for use, could be pre-formed in the cartridge.

[0069] After use, the cartridge 50 is removed from the gun anddiscarded. Because the cartridge 50 contains a filter, there is no needfor the supplier to filter the paint before it is loaded into thecartridge. If, however, the paint is pre-filtered, then the filter inthe cartridge 50 can be omitted.

[0070]FIG. 15 illustrates an alternative form of paint pot 40 for aspray gun 1, which is entirely disposable. The paint pot 40 is generallysimilar to the pot 30 shown in FIG. 10 except that the container 12 isreplaced by a disposable container 41, described below, and the liner 13is omitted.

[0071] The container 41 of FIG. 15 can be any conventional disposablecontainer suitable for containing paint and for attachment to the paintpot lid 42. The container 41 may, for example, be formed from a thinplastic material, preferably translucent (as shown) so that the contentsof the container are visible and preferably having markings 43 on theside walls to enable the volume of the contents of the container to bedetermined. An air hole 44 is formed in the base of the container,together with some means for closing the air hole when desired. Thatmeans may take the form of a strip of adhesive tape (not shown) which ispeeled back to open the hole 44 and can be re-adhered to close the holewhen required. Alternatively, a flip-top closure or some simplehand-operated valve mechanism may be provided. The container 41 has anexternal screw-thread at its open end, for attachment of the lid 42which is generally similar to the lid 33 of FIG. 10 and is likewiseshaped, at its upper end 42A, for attachment to a spray gun (ifnecessary by means of a suitable adapter). The lid 42 may be formed fromthe same material as the container 41 and, as shown, may also betranslucent. A flat filter mesh 45, which is also disposable, extendsacross the mouth of the container 41. The mesh 45 may be a separateitem, held at its periphery between the lid 42 and the container 41, orit may be formed integrally with the lid.

[0072] To use the pot 40, the lid 42 and filter mesh 45 are removed fromthe container 41 which is then filled with paint (care being taken thatthe air hole 44 in the base of the container is closed). It isunnecessary to strain the paint when it is put into the container 41and, as described above, it is possible to mix the paint in thecontainer thereby avoiding the need for a separate receptacle for thatpurpose. The lid 42 and mesh 45 are then put back in position on thecontainer 41, the lid 42 is attached to the (inverted) spray gun 1 whichis then returned to its normal position, and the air hole 44 in the baseof the container is opened. The spray gun 1 can now be used in the usualway. On completion of the spraying operation, the air hole 44 isclosed-off again, the pot 40 is detached from the gun 1 and may then bediscarded leaving only the gun to be cleaned. Before the pot 40 isdetached, the spray gun 1 can be re-inverted and the trigger 5 of thegun operated to allow excess paint remaining in the gun to drain backinto the pot. In either case, if sufficient paint remains in the pot 40,the pot could be re-sealed (instead of being discarded) and used again.

[0073] Advantageously, the container 41 of the pot is formed so that itcan be collapsed after use. In some cases, it may be possible for thelid 42 also to be collapsible.

[0074] As an alternative, the lid 42 could be a reusable component andwould be cleaned with the gun. With an arrangement of that type, it ispossible for the disposable container 41 to be supplied as a cartridgealready filled with paint and sealed by a cover which would simply beremoved before the container is attached to the lid 42. The filter mesh45 could be either a disposable or a reusable component. As a furtheralternative, the container 41 and lid 42 together could be supplied as acartridge sealed by a removable cover, at the upper end 42A of the lid,which would be removed before the cartridge is attached to the gun. Inthat form, the cartridge is similar to the cartridge 50 of FIG. 14.

[0075] Through an appropriate selection of the dimensions of the lid 42of the paint pot 40, it is possible for the one lid 42 to be used withcontainers 41 of different sizes. The user would then select, in eachcase, the container 41 that contains the most suitable amount of paint.It may also be desirable for a range of filters 45 having different meshsizes to be provided so that the user can select the mesh size that isbest suited to the type of paint that is being used. It is not essentialfor the filter mesh 45 to have the form and/or location shown in FIG.15: it could, for example, have a conical form as shown in FIG. 16and/or it could be located in the outlet of the lid 42, as shown in FIG.17. Alternatively, the filter 45 can be omitted if the paint is filteredbefore it is put into the container 41, or if the presence ofcontaminants in the paint is unimportant.

[0076] The lid 42 need not have the exact shape shown in FIG. 15 andcould, for example, be replaced by a push-in lid in combination with ascrew-on collar as shown in FIG. 2.

[0077] When the container 41 (with or without the lid 42) is supplied asa cartridge containing paint (or other coating material) it may bedesirable in some cases for the paint/coating material to be containedwithin a sealed collapsible liner within the cartridge. That may, forexample, be desirable if it is necessary for the paint/coating materialto be kept isolated, for example from the air or from light, until ithas been sprayed onto the surface to be coated. The air hole 44 in thecontainer 41 can then remain open all the time, or may be omitted if thecontainer 41 itself is not airtight.

[0078] Depending on the shape of the container 41, it may be desirableto provide a holder in which the container can be located to ensure thatit will not be knocked over. One suitable holder 50, shown in FIG. 18,comprises container portion 51 which is of similar shape to, butslightly larger than, the container 41 and is provided with an enlargedbase 52. The container 41 is placed in the container portion 51 toensure that it remains upright while it is being filled and/or attachedto the spray gun 1.

[0079] Although the above description refers to a paint spray gun, itshould be understood that it applies also to other types of spray gunincluding, for example, guns of the type which are attached to waterhoses (rather than air supply lines) for spraying substances such asgarden chemicals. The description also applies to suction-feed guns,i.e. guns in which the liquid outlet from the reservoir is located atthe top of the reservoir when the gun is in use and liquid is drawn fromthe reservoir through a supply tube by the action of the compressed airor other pressurized fluid flowing through the gun. In that case, when aliner is provided for the reservoir, the construction of the linerand/or the supply tube should be such that the liner can collapsewithout blocking the supply tube. For example, a short supply tube canbe used provided all air is exhausted from the liner before the gun isused. Alternatively, a flexible supply tube could be used, which willcollapse with the liner. As a further alternative, a modified linerwhich does not have a rigid base could be used, so that the linercollapses in a different manner from the liner 13 of FIG. 2. Since thereservoir of a suction-feed gun is not inverted during use, as in agravity-feed gun, it is possible to omit the air hole in the reservoir,provided the connection between the reservoir and the gun permits air toenter the space between the reservoir and the liner.

[0080] Returning now to the paint pot 11 of FIG. 2, the liner 13 willnow be described in greater detail, together with a method by which itcan be produced. The liner, shown in isolation in FIGS. 19 and 20, ispreferably transparent and is thermo-formed from a single piece ofplastics material, preferably polyethylene or polypropylene. The shapeof the liner is dictated by the internal shape of the container 12. Thecomparatively rigid base 13A is circular and the liner 13, like theinside of the container 12, is generally cylindrical but tapers inwardsslightly from the mouth towards the base 13A. The rim portion 14, likethe base, is also comparatively rigid but the side walls 13B areflexible and, as already described, can be made to collapse.Nevertheless, the liner 13 is capable of standing, unsupported, on thebase 13A with the side walls 13B extended and upright as shown in FIG.19. When the liner 13 collapses, the comparatively rigid base 13Aretains its form but moves towards the rim portion 14 of the liner as aconsequence of the collapse of the side walls 13B, as illustrated inFIG. 20. The side walls 13B collapse in a similar fashion to a plasticbag without being ruptured (e.g. by splitting, tearing or cracking).

[0081] In one form, the liner has a height of about 110 mm, a diameterat its base 13A of about 78 mm and a diameter at its mouth (excludingthe rim portion 14) of about 86 mm. The base has a thickness of about400 μm, the rim portion 14 has a thickness of about 900 μm, and the sidewalls 13B have a thickness of about 150 μm. In another form, the linerhas the same height and the same diameters at its base and mouth but thebase has a thickness of about 300 μm, the rim portion has a thickness ofabout 200 μm, and the side walls 13B have a thickness in the range offrom 50 to 250 μm.

[0082] A method of producing a liner as shown in FIG. 19 will now bedescribed with reference to FIG. 21 (a)-(c).

[0083] A sheet 60 of low density polyethylene (LDPE), approximately250×225 mm and 0.5 mm thick, was clamped at its periphery in themoulding frame 61 of a vacuum-forming machine. The LDPE material iscommercially available from, for example, Plastech Extrusions Ltd. ofWidnes, Cheshire, England and the vacuum-forming machine used was themodel “FLB 725” from C.R.Clarke and Company Limited of Ammanford,Carmarthenshire, Wales. It will be appreciated, however, that anysuitable plastics material could be used and that the method could becarried out using any suitable thermo/vacuum-forming machine.

[0084] After the sheet 60 had been placed in position, the bank ofheaters 62 of the vacuum-forming machine was moved into position abovethe sheet (as shown in FIG. 21(a)), and the sheet was heated to a soft,pliable, state suitable for vacuum-forming. The fact that the sheet hadreached the appropriate temperature could be seen by the change in itsappearance from milky to transparent.

[0085] The bank of heaters 62 was then removed and the mould platen 63was moved upwards from below the sheet 60, bringing the mould 64 intocontact with the sheet to deform the latter in an upwards direction. Atthis time, the vacuum pump of the machine was switched on to remove airfrom beneath the sheet 60. The upward movement of the mould platen 63was continued until the platen reached the top of its stroke, where itseals against the frame 61 holding the sheet 60 (FIG. 21(b)). The mould64 had a shape corresponding to the internal shape of the container 12of the spray gun paint pot 11.

[0086] Operation of the vacuum pump was continued with the mould platensealed against the frame 61 and the pressure difference created betweenthe upper and lower sides of the sheet 60 caused the latter (which wasalready in contact with the top of the mould 64) to move down intocontact with the sides of the mould (FIG. 21(c)). The mould platen 63was then moved away from the cooled sheet 60 leaving a moulded portion65 having the desired shape of the liner 13 and without any pleats,corrugations, seams, joints or gussets, or any groove at the internaljunction of the side walls 13B with the base 13A. Following removal fromthe frame 61, the sheet 60 was trimmed around the mouth of the mouldedportion 65 to form the rim 14 of the liner 13. The width of the rim 14is determined by the location at which the sheet 60 is trimmed at thisstage, and can be adjusted as required.

[0087] The above-described process was found to yield a moulded portion65 (and hence a liner 13) in which that part of the plastics sheet 60that had been in contact with the sides of the mould 64 during theforming process was substantially thinner than the part that had been incontact with the top of the mould. The process differs from aconventional vacuum-forming process which would aim to eliminate, as faras possible, any differences in thickness in the moulded portion 65 and,to that end, would include the additional step of applying air pressureto the underneath of the heated sheet 60, after step (a) of FIG. 21, tocause the sheet to adopt a dome shape before the mould platen 63 sealsagainst the frame 61: the thickness of the sheet would then becomparatively even when it moves into contact with the mould 64 in step(c) of FIG. 21. Generally in the process illustrated in FIG. 21, for agiven size of sheet 60, the size of the mould 64 has been found toaffect the thickness of the sides of the resulting liner 13 more thanthe base. In other words, if the size of the mould 64 is increased, thethickness of the base of the resulting liner 13 will be about the samebut the sides of the liner will be much thinner. On the other hand, ifthe size of the mould is decreased, it may be found that a point isreached at which longitudinal creases appear in the sides of the liner13.

[0088] If a further reduction is required in the thickness of the sheet60 where it contacts the sides of the mould 64 in step (c) of FIG. 21,the sheet 60 can be located between two thin metal plates 66 (FIG. 22)when it is clamped in the frame 61 of the forming machine, each metalplate 66 having a hole 67 in the location of the mould 64 and larger insize than the largest cross-section of the mould. The plates 66 are alsoclamped in the frame 61 and the process of FIG. 21 is then repeated. Theeffect of the plates 66 is that only the central portion of the sheet 60is exposed directly to the heaters 62 and is drawn over the mould 64when the latter has been moved upwards (in this case, through the holes67 in the plates 66). In that way, less of the sheet 60 is used in theformation of the moulded portion 65 and the resulting liner 13 will havea slightly thinner base 13A and rim 14 and substantially thinner sidewalls 13B. It is also possible to obtain a comparable result by usingonly the upper plate 66 shown in FIG. 22.

[0089] As a modification of the process illustrated in FIG. 22, theplastics sheet 60 can be in the form of a circular disc of materialwhich is clamped at its periphery between the two plates 66. Dependingon the size of the disc, the clamped periphery may then form the rim 14of the liner 13 and there may be no excess material to be trimmed away.

[0090] It has been found that a liner 13 produced by a process asdescribed with reference to FIGS. 21 and 22 will collapse as describedwith reference to FIG. 20 when used in the spray gun reservoir 11 ofFIG. 2. The liner 13 can also be collapsed by hand by pushing the base13A of the liner towards the rim 14. It has been found that the liner istypically capable of standing unsupported on its base 13A and thisfeature, although not essential to the use of the liner in the spray gunreservoir 11, may be of use for storage purposes. The liner has nopleats, corrugations, seams, joints or gussets, and no groove at theinternal junction of the side walls 13B with the base 13A: consequently,there are no internal locations in which material within the liner canbecome trapped. The base 13A of the liner will, of course, occupy somespace at the base of the container 12 of the spray gun reservoir 11 andthe markings on the wall of the container 12 need to be positioned totake account of that fact.

[0091] Although the liner 13 of FIG. 19 has been described for usespecifically in the paint pot 11 of FIG. 2, the same or a similararticle can be used in other ways (subject, if necessary to appropriatedimensional changes). For example, an article of the type illustrated inFIG. 19 can also be used as a liner in many forms of receptacle otherthan a spray gun reservoir. It is often desirable to provide areceptacle with a disposable liner, for example to keep the receptacleclean, to facilitate cleaning, or to protect the receptacle or itscontents. A liner of the type illustrated in FIG. 19 can be used for anyof those purposes and is especially useful in receptacles in whichsubstances are mixed together because there are no locations on theinside of the liner in which material can become trapped and remainunmixed.

[0092] An article of the type illustrated in FIG. 19 can, for example,be used as a liner in a receptacle intended for paint mixing in avehicle body shop, in which case it will provide an attractivealternative to the disposable drinking cups which are often employed forthat purpose. Prior to painting the repaired portion of a vehicle in abody shop, the repairer must mix-up a batch of paint of the requiredcolour, matching the colour of the surrounding portion of the vehicle.The various components for a batch of paint should be measuredaccurately, either by volume or by weight, into a suitable receptacle inwhich they are mixed together thoroughly before being used. If themixing is less than thorough, or if the receptacle is not absolutelyclean, the colour/quality of the batch of paint (and, consequently, thequality of the repair) may be affected.

[0093] To enable paint mixing to be carried out conveniently, buteffectively, a liner of the type illustrated in FIG. 19 can be used witha measuring vessel 70 as shown in FIG. 23. The measuring vessel 70 is inthe form of a pitcher having a spout 71 in a shaped rim 72 and a handle73. The pitcher is provided with markings 74 on the side walls, enablingthe volume of the contents of the pitcher to be determined. Using themethod already described with reference to FIG. 21, liners of the typeshown in FIG. 19 can be produced to fit accurately inside the pitcher 70and, by utilizing such a liner, the various components for a batch ofpaint can be assembled and mixed together in the pitcher 70 withoutactually coming into contact with the latter.

[0094] A liner 75 suitable for use in the pitcher 70 is illustrated inFIG. 24. The liner 75 has a shape corresponding to the interior of thepitcher 70 and is generally similar to the liner 13 illustrated in FIG.19 except that the thicker, outwardly-extending, rim portion 14 of thelatter is omitted and the side walls 76 of the liner 75 include a shapedrim 77 corresponding to the rim 72 and spout 71 of the pitcher. Becausethe liner 75 fits the inside of the pitcher 70 exactly, the possibilitythat it will be punctured by the mixing implement when paint is beingmixed in the pitcher is minimized. In addition, because there are nolocations in the interior of the liner in which material can becometrapped, there is no barrier to the effective mixing of all the materialthat is measured into the pitcher. When the paint has been mixed andtransferred from the pitcher 70 (for example, to the paint pot of aspray gun), the liner 75 is removed, preferably collapsed as shown inFIG. 20, and thrown away, leaving the pitcher 70 clean and ready forfurther use.

[0095] Because the base 78 of the liner 75 will occupy some space at thebottom of the pitcher 70, the markings 74 on the side walls of thepitcher may need to be positioned to take account of that fact. It mayalso be desirable, depending on the shape of the pitcher 70, to providean extension at the top of the liner 75 which can be folded back overthe rim 72 of the pitcher. Alternatively, or in addition, it may bedesirable to seal the liner 75 to the pitcher 70 during use, for exampleby providing some form of shaping on the liner and the pitcher so thatthey can be snap-fitted together at the rims 77, 72.

[0096] Although it is desirable that the liner 75 of the pitcher 70should be collapsible so that it occupies less space after use, that isnot absolutely essential. Moreover, since the shape of the liner 75 isdetermined by the shape of the interior of the receptacle 70 in which itis to be used, there may be cases in which the liner is not capable ofstanding, unsupported, outside the receptacle.

[0097] As a further alternative, an article of the type shown in FIG. 19can be used simply as a container in which case it has the advantagethat, although the walls 13B are comparable in flexibility to a plasticbag, the container will stand upright, without support, while it isbeing filled and also afterwards. The container can be of anyappropriate size and can be used to contain many different types ofitems, including for example powders and liquids, or simply as analternative to the plastic/paper bags provided to customers byretailers. In each case, the container has the advantage that there areno internal locations in which material within the container can becometrapped. Depending on the contents of the container, it may be desirableto be able to close the container mouth, in which case some appropriateform of closure can be provided. The closure may, for example take theform of an internal rib on the inside of the container around one halfof the mouth, and a mating groove also on the inside of the containeraround the other half of the mouth into which the rib can be pressed toclose the container. The flexibility of the container walls 13Badditionally allows the walls to be pressed down around the contents,thereby reducing the air space within the container if required.

[0098] After use, when it is required to dispose of the container, theside walls 13B can be collapsed by hand by pushing the rim 14 towardsthe base so that the container (now in the form illustrated in FIG. 20)requires less space for disposal. As already mentioned, the side walls13B collapse in a similar fashion to a plastic bag without beingruptured (e.g. by splitting, tearing or cracking).

[0099] It will be appreciated that there are many other possible usesfor articles of the type shown in FIG. 19. A liner of that type could,for example, be used simply as a liner for a refuse bin where it wouldoffer the advantage of being a better fit inside the bin than aconventional bag-shaped liner, and of being easier to handle whenremoved from the bin because it will stand upright on the base 13A.Similar liners could also be used in buckets or other containers formaterials that harden comparatively quickly (for example glue, wax orplaster): in some cases, material such as plaster is actually soldtogether with a mixing bucket, in which case a supply of liners could beincluded in the package. In some circumstances, it might be appropriateto have a plurality of liners, stacked one inside another, in positioninside a receptacle so that when one liner is removed the next isalready in position. Moreover, since the receptacle is intended tocontain a liner, it is not essential for the walls of the receptacle tobe solid: the receptacle could, for example, have the form of aframework for containing the liner.

[0100] Generally, in an article of the type shown in FIG. 19, the base13A is typically at least 25 μm thick, more typically at least 100 μmthick. The side walls 13B are thin in comparison to the base 13A, to theextent that they can be collapsed as described to facilitate disposal ofthe liner/container: typically, the thickness of the side walls 13B isless than half the thickness of the base 13A and may be less than onefifth the thickness of the base. Depending on the materials used, andthe intended use of the liner/container, the side walls 13A will usuallybe less than 250 μm thick.

[0101] For certain uses of an article of the type shown in FIG. 19, therim portion 14 may not be essential and can be omitted (as in the linerof FIG. 24). If no rim 14 is required the sheet 60 of FIG. 21(c) would,of course, be trimmed immediately adjacent the mouth of the mouldedportion 65. It has been found that the self-supporting nature of theliner/container can be retained even if the rim portion 14 is omitted.

[0102] It should also be noted that the base 13A of a container/liner ofthe type shown in FIG. 19 need not be circular but could have anothershape, for example rectangular or triangular. In the case of a liner fora receptacle, that shape may be dictated by the shape of the receptacleparticularly if the liner is required to fit the interior of the latter.In some cases, the base need not be rigid.

[0103] It will further be appreciated that the process illustrated inFIGS. 21 and 22 is not restricted to the production of liners for use inthe paint pots of spray guns and can be adapted to produceliners/containers for other purposes. It will be appreciated that theprocess requires the mould 64 to have a slightly tapered shape with thelargest cross-section being at the lower end (as seen in FIGS. 21 and22) to allow the sheet 60 to be removed when the forming operation iscomplete. When the process is used to produce of a liner which isrequired to fit inside a container, that, in turn, requires that thecontainer should be similarly tapered internally. The liner/containermay be formed from any suitable thermoplastic material capable offorming a thin film which is impervious to the materials it is intendedto contain. In some cases, it may be desirable to use a material whichis in the form of a laminate. For certain applications, such as foodpackaging, plastics with a low gas-permeability may be preferred. Formost applications, however, polyolefins such as polyethylene orpolypropylene are preferred since these are relatively inexpensive, arereadily thermo-formable, and are inert to most aqueous and organicfluids.

1. A liner for use in the reservoir of a spray gun, the liner beingformed from a thermoplastic material, the liner having a comparativelyrigid base, side walls, or wall in the case of a cylindrical liner,which are thin in comparison to the base and are collapsible, said linerbeing capable of standing unsupported on the base with the side walls,or wall, extended and upright.
 2. The liner of claim 1 in combinationwith a lid that fits sufficiently tightly on the liner that the lid andliner can be removed from the reservoir together.
 3. The liner of claim1 of which the thickness of the side walls is less than half thethickness of the base.
 4. The liner of claim 1 which is generallycylindrical in shape but tapers inwards slightly towards the base. 5.The liner of claim 1 having an outwardly-extending rim portion shaped tosit on an edge of an opening in the spray gun reservoir.
 6. The liner ofclaim 5 of which the rim portion is substantially thicker than the sidewalls of the liner.
 7. The liner of claim 1 formed from low densitypolyethylene or polypropylene.
 8. The combination of a receptacle usefulas a spray gun reservoir and the liner of claim 5 which liner is a closefit within the reservoir.
 9. The liner of claim 1 of which the sidewalls, or wall, are sufficiently thin in comparison to the base that theside walls collapse in use causing the liner to collapse in alongitudinal direction.
 10. A fluid reservoir for attachment to a spraygun, the reservoir having a removable lid which is located in an openingin the reservoir and in which is formed a fluid outlet for thereservoir; the reservoir including a removable, collapsible, liner whichhas a shape corresponding to, and is a close fit within, the reservoir;wherein the liner is secured to the reservoir by the lid at theperiphery of the opening and is removable from the reservoir togetherwith the lid.
 11. A fluid reservoir as claimed in claim 10, including afilter for fluid leaving the reservoir, the filter also being removablefrom the reservoir together with the lid.
 12. A spray gun comprising: afluid reservoir; a removable, collapsible, liner which, prior to addinga fluid to the liner, has a shape corresponding to, and is a close fitwithin, the interior of the reservoir; a lid for the reservoir, and aspray nozzle for dispensing fluid from within the liner; wherein theliner collapses when fluid is withdrawn from within the liner duringoperation of the gun, and in which the combination of reservoir andliner has a fill opening which is inverted when connected to the spraygun in normal operation with fluid passing from within the liner to thespray nozzle, and the liner is removable from the reservoir togetherwith the lid, the lid engaging the liner by means selected from push-fitwith the liner, barbs on the lid, the lid being formed as an integralpart of the liner, a hinge joint, and a snap fit between a rib on theliner and a groove in the lid.
 13. The spray gun of claim 12 furthercomprising a removable filter positioned to filter fluid passing fromwithin the liner to the spray nozzle.
 14. The spray gun of claim 13 inwhich the filter is located within the reservoir and is removable fromthe reservoir together with the lid.
 15. The spray gun of claim 12 inwhich the outlet for fluid from within the liner to the spray nozzle isformed in the lid.
 16. A method of preparing a gravity fed liquidspraying apparatus comprising the steps of: a) providing a containerhaving a base and sidewalls, or a sidewall, extending from the base toan open end; b) with the container standing upright on the base, addingliquid to the container through the open end; c) attaching to thecontainer a lid having an outlet, the combination of the lid andcontainer comprising a reservoir; d) connecting a spray gun to theoutlet of the lid; e) inverting the combination of the spray gun andreservoir so that the reservoir is above the spray gun; and f) openingan air hole in the container.
 17. The method of claim 16 furthercomprising the step of: g) closing the air hole upon completion ofspraying, inverting the combination of spray gun and reservoir so thatthe spray gun is above the reservoir and disconnecting the spray gunfrom the outlet.
 18. The method of claim 17 further comprising the stepof: h) sealing the reservoir to store unused liquid.
 19. The method ofclaim 16 further comprising locating a filter in the lid to filterliquid withdrawn from the reservoir in use.
 20. A method of preparing agravity fed liquid spraying apparatus comprising the steps of: a)providing a liner having a base and sidewalls, or a sidewall, and anopening and being capable of standing unsupported on the base with theside walls extended and upright; b) placing the liner in an outercontainer; c) with the liner standing upright on the base, adding liquidto the liner through the opening; d) attaching to the combination of theouter container and liner a lid which covers the opening of the linerand has an outlet, the combination of liner, outer container and lidcomprising a reservoir; e) connecting a spray gun to the outlet of thelid; f) inverting the combination of the spray gun and reservoir so thatthe reservoir is above the spray gun.
 21. The method of claim 20 inwhich the lid engages the liner so that the liner can be lifted from theouter container together with the lid and said method further comprises:g) removing the liner from the outer container together with the lid.22. The method of claim 20 further comprising releasably securing theliner in the outer container.
 23. The method of claim 20 furthercomprising locating a filter within the combination of the reservoir andlid to filter liquid withdrawn from the reservoir in use.
 24. The methodof claim 20 in which the side walls of the liner are thin in comparisonto the base of the liner, and the method further comprises spraying theliquid, said liner collapsing during the spraying.
 25. A method ofpreparing a gravity fed liquid spraying apparatus comprising the stepsof: a) providing a sealed container containing liquid and having anoutlet end for attachment to a spray gun apparatus; b) opening theoutlet end to allow flow of liquid to the spray gun; c) connecting aspray gun apparatus to the outlet of the sealed container while theoutlet end is above the liquid in the container; d) inverting thecombination of the spray gun and sealed container so that the sealedcontainer is above the spray gun; and e) opening an air vent in thesealed container.